The purpose of the study is to test the feasibility and acceptability of a mindfulness- and acceptance-based smartphone app (MABSA) intervention for college student veterans with posttraumatic stress disorder (PTSD) symptoms. The study will use a randomized controlled trial design of two groups: intervention group of about 30 participants with PTSD and wait-list control group of about 30 participants. The duration of the MABSA intervention is 6 weeks. The following are the outcomes to be measured: resilience, PTSD, mindfulness, experiential avoidance, and rumination.

The objective of the proposed study is to evaluate the feasibility of the Mindfulness/Acceptance-Based Smartphone App (MABSA) intervention in a randomized controlled trial (RCT) environment and to obtain generalized information (i.e., initial efficacy, recruitment, retention, adherence, satisfaction, and usability of the refined intervention). The expected results will provide the foundation for a prospective, fully powered, larger-scale RCT study. We previously developed the MABSA and pilot tested it in a single-arm study. Our central hypothesis is that the refined MABSA intervention would improve intervention satisfaction, app usability, and adherence and positively affect resilience, PTSD, mindfulness, experiential avoidance, and rumination. The specific aims of the proposed study are outlined below.

AIM 1: To refine the previously developed MABSA intervention. The 6-week smartphone-delivered program will involve (1) daily audio-guided meditations on various mindfulness and acceptance exercises constructed based on the principles of acceptance and commitment therapy; (2) weekly support and feedback through phone calls and/or texting the intervention facilitators; and (3) ecological momentary assessment (daily monitoring of PTSD and resilience) to monitor the progression of treatment response (i.e., the trajectory of resilience and PTSD recovery). We will obtain qualitative feedback on program content and format through a pilot test of the prototype with a group of eligible college student veterans (N = 4). Upon revising the intervention based on participants' feedback, we will develop the intervention protocol manual for the RCT.

AIM 2: To test the feasibility and acceptability of the refined MABSA intervention in a small-scale RCT for a prospective, fully powered, larger-scale RCT study. The small-scale RCT study will involve the following two groups of college student veterans: (1) the MABSA intervention group (N = 30) and the waitlist control group (N = 30). Upon collecting the data on recruitment, retention, adherence, intervention satisfaction, and app usability, we will determine the preliminary efficacy based on the following five outcomes: resilience, PTSD, mindfulness, experiential avoidance, and rumination. Qualitative feedback on the facilitators of and challenges to recruitment, retention, and adherence will be collected via exit interviews.

Inclusion Criteria:

• (1) aged 18 years old or older, (2) currently registered as an undergraduate or graduate student, (3) has previous active military service from any U.S. military service branch, (4) has at least daily access to their own Apple iPhone (version 5 or later) or Android phone, and (5) have posttraumatic stress disorder (PTSD) symptoms (must have a score of 33 or above on the PTSD Checklist for DSM-5)

Exclusion Criteria:

• (1) Those who have a score of 32 or below on the PTSD Checklist for DSM-5 and (2) Those who have a cognitive impairment such as dementia-related disorders.